1. Field of the Invention
The present invention relates to B cell differentiation factor (hereafter referred to as "BCDF") having activity in humans, a gene corresponding to human BCDF polypeptide, biotic cells having incorporated therein the gene, a method for production of the BCDF using the biotic cells as well as an immunotherapeutic composition comprising human BCDF as an effective component.
2. Description of the Related Art
Mature human BCDF is a material that was first discovered as a discrete substance by the present invention. It can be widely utilized as a therapeutic composition for immunodeficiency diseases.
European Patent Application 0220574 describes certain so-called interferons having an amino acid sequence related to BCDF of this invention. However, the protein disclosed in EP 0220574 is longer than mature human BCDF, and contains at least a signal peptide attached thereto. The structure of mature human BCDF was not appreciated before the present invention. Also in contrast to the polypeptide of EP 0220574, the present polypeptides do not have the anti-viral activity described in EP 0220574.
Mature B cells activated by stimulation with an antigen are caused to proliferate by the aid of T cells, but it is known that one or more T cell-derived differentiation-inducing substances are necessary to finally differentiate B cells to reach antibody-producing cells. The presence of such substances has been substantiated by R. W. Dutton et al., Transplant. Rev., 23, 66 (1975) and, A. Schimpl and E. Wecker et al., Nature N. Biol., 237, 15 (1972). They have found that the supernatant after culturing a mouse lymphocyte mixture or the supernatant after culturing mouse lymphocytes stimulated with an antigen or mitogen can amplify a primary immune response of mouse lymphocyte mass from which mouse T cells are removed or of nude mouse-derived lymphocytes to sheep red blood cells and have given the name of T cell replacing factor, namely TRF, to the active substance having such an activity. Since then, TRF has been defined to be a humoral factor which acts on B cells in such a manner that does not require any consistency in major histocompatibility gene complex (hereafter simply referred to as MHC) non-specifically to antigen, does not induce proliferation of B cells but induces differentiation of B cells to antibody-producing cells.
After that, functional evidence showing the presence of such a B cell differentiation factor has been accumulated and the presence of a human differentiation factor analogous to the one in mice has been suggested. At present, the factor defined as described above that differentiates B cells into antibody-producing cells has been collectively termed BCDF.
As such, BCDF plays an important role in the function of antibody production of B cells in vivo in humans.
Lymphokines, which are soluble proteins having biological and pharmacological activity, act to regulate immune response mechanisms of the body in vivo in a trace amount. The utility of lymphokines as anti-tumor agents, an anti-viral agents, anti-bacterial agents, immunodeficiency therapeutic agents and autoimmune disease therapeutic agents has been expected due to the nature of these immunoactive substances (Adv. in Immunopharm., 507, 1980). BCDF in accordance with the present invention is a lymphokine and, from this point of view, BCDF is expected to be applicable as a medical drug.
To obtain BCDF, there has been hitherto adopted a method which comprises separating normal T cells from human peripheral blood and stimulating the T cells with mitogen to produce BCDF. According to this method, many problems arise in that it is difficult to obtain T cells in a sufficient amount; toxic mitogens harmful to BCDF contaminate because mitogens are used and it is difficult to remove them; it is necessary to supplement serum components such as fetal bovine serum, etc. in culture of T cells and BCDF cannot be sufficiently separated from these supplemented proteins so that failure to give pure BCDF becomes an obstacle to medical use of BCDF. BCDF could not thus be produced industrially. There is also reported a method which comprises cell fusion of human T cells with human cancer cells to give human T cell hybridomas and producing BCDF using the hybridomas (Okada et al., J. Exp. Med., 157, 583 (1983)). However, human hybridomas often tend to reduce their lymphokine productivity during culture, so BCDF-producing human hybridomas that withstand practical use are still unknown.